Sensitizing solution for electroless plating and electroless plating method

ABSTRACT

Provided is a sensitizing solution for electroless plating which can easily dissolve an Sn compound therein without the use of acid, and thus can be used for a long period of time without impairing the uniformity of a metal plating coating. The sensitizing solution for electroless plating is a sensitizing solution for electroless plating including: an Sn compound; and a solvent, wherein the solvent contains 10 vol. % or more of a water-soluble alcohol. In addition, provided is an electroless plating method including: a pretreatment process of immersing a body to be plated into a pretreatment solution; and a plating process of immersing the body to be plated after being subjected to the pretreatment process into a plating solution, wherein the sensitizing solution for electroless plating according to the invention is used as the pretreatment solution.

TECHNICAL FIELD

The present invention relates to a sensitizing solution for electrolessplating and an electroless plating method, and more particularly, to asensitizing solution for electroless plating which can be used for along period of time without impairing the uniformity of a metal platingcoating, and an electroless plating method using the same.

Priority is claimed based on Japanese Patent Application No.2008-222819, filed on Aug. 29, 2008, the content of which isincorporated herein by reference.

BACKGROUND ART

An electroless plating method is a method of forming a metal platingcoating on a body to be plated which is made of a non-conductivematerial such as glass, ceramic, or plastic other than metals, and iswidely used for decorations, electromagnetic shielding, wiringtechnology such as printed-circuit boards and large-scale integratedcircuits, and the like.

Typically, in a case where a metal plating coating is formed on a bodyto be plated using the electroless plating method, pretreatment isperformed to cause a plating catalyst to adsorb onto the body to beplated. As the pretreatment, in general, a sensitizing treatment forsupplying an adsorbent material to the body to be plated to acceleratethe adsorption of the plating catalyst onto the body to be plated, andan activation treatment for causing the plating catalyst to adsorb ontothe body to be plated are performed.

With regard to the sensitizing treatment and the activation treatment,there are a “two-solution method” in which they are separately performedusing different treatment solutions and a “one-solution method” in whichthey are simultaneously performed using a single treatment solution. Theone-solution method is widely used in industry because the number ofmanufacturing processes can be reduced compared to the two-solutionmethod. In addition, the one-solution method is particularly preferablyused in a case where the body to be plated is made of plastic. As atreatment solution of the one-solution method, a Sn—Pt mixed catalyst isgenerally used.

The two-solution method provides excellent adhesion of the metal platingcoating onto the body to be plated compared to the one-solution methodin a case where the body to be plated is made of glass or ceramic.Particularly, for the wiring technology such as printed-circuit boardsand large-scale integrated circuits which requires high adhesion of themetal plating coating onto the body to be plated, the two-solutionmethod is very suitable.

As a sensitizing solution used in the two-solution method, ahydrochloric acid aqueous solution of stannous chloride (SnCl₂) isknown. In this sensitizing solution, Sn²⁺ ions included in thesensitizing solution are oxidized and become Sn⁴⁺ and thus aredeactivated. Sn²⁺ ions are easily oxidized and become Sn⁴⁺, so that thesensitizing solution has a problem in that the applicable time is about20 hours to 40 hours and thus is short. When the applicable time of thesensitizing solution is short, the uniformity of the metal platingcoating is easily damaged, resulting in variation of quality. Inaddition, a renewal frequency of the sensitizing solution is increased,and thus an increase in time and effort and an increase in costs result,which is not preferable in industry.

In order to solve this problem, a sensitizing aqueous solution forelectroless plating which is a sensitizing solution that contains anadsorbent material to be adsorbed onto a body to be plated throughimmersion of the body to be plated in the sensitizing solution, suchthat an adsorption site for causing a catalyst used for electrolessplating to adsorb onto the surface of the body to be plated is formed onthe surface of the body to be plated, and in which an absorbentoxidization and colloidization inhibitor that inhibits oxidization ofthe adsorbent material in the aqueous solution, inhibits colloidizationand dispersion of colloidal materials in the aqueous solution, and isnot easily soluble in water is added, is proposed (for example, refer toPatent Literature 1).

In addition, as a technique for providing a sensitizing solution whichhas a long life span, a sensitizing solution for electroless platingwhich is a strong acid aqueous solution containing Sn²⁺ ions, and inwhich, in the aqueous solution, halide ions are not practicallycontained, or the molar concentration of the halide ions is three timesor less than the total molar concentration of the Sn²⁺ ions and Sn⁴⁺ions, is proposed (for example, refer to Patent Literature 2).

In addition, in order to provide a sensitizing solution having a longlife span, increasing the concentration of stannous chloride (SnCl₂)contained in the sensitizing solution to be high is considered. In orderto increase the concentration of stannous chloride (SnCl₂) contained inthe sensitizing solution to be high, the concentration of hydrochloricacid added to dissolve stannous chloride (SnCl₂) in the sensitizingsolution has to be increased. However, it is known that when theconcentration of hydrochloric acid contained in the sensitizing solutionis increased, the life span is shortened (for example, refer toNon-Patent Literature 1).

PATENT LITERATURE

-   [PTL 1] JP-A-2007-63646-   [PTL 2] JP-A-2005-248287

NON-PATENT LITERATURE

-   [NPL 1] Himeji Institute of Technology, MATSUDA HITOSHI: Journal of    The Surface Finishing Society of Japan Vol. 55 (2004), No. 4, p. 281

SUMMARY OF INVENTION Technical Problem

In the technique according to the related art, the applicable time ofthe sensitizing solution cannot be sufficiently lengthened. In addition,in the sensitizing solution according to the related art, when an Sncompound of stannous chloride (SnCl₂) or the like is used as theabsorbent material for accelerating the adsorption of the platingcatalyst onto the body to be plated, the compound needs to be dissolvedin the sensitizing solution using acid such as hydrochloric acid. Acidcorrodes a manufacturing apparatus or the like and thus it is preferablethat the use thereof be avoided.

In order to solve the problems, an object of the invention is to providea sensitizing solution for electroless plating which can easily dissolvean Sn compound without the use of acid, and thus can be used for a longperiod of time without impairing the uniformity of a metal platingcoating.

Another object of the invention is to provide an electroless platingmethod capable of, by using a sensitizing solution that can be used fora long period of time, obtaining excellent uniformity of a metal platingcoating such that variations in quality rarely result, and capable ofreducing a renewal frequency of the sensitizing solution, therebyobtaining industrially high productivity.

Solution to Problem

In order to accomplish the objects, the invention employs the followingconfigurations:

(1) A sensitizing solution for electroless plating including: an Sncompound; and a solvent, wherein the solvent contains 10 vol. % or moreof a water-soluble alcohol.

(2) The sensitizing solution according to (1), wherein the water-solublealcohol is at least one kind selected from the group consisting ofmethanol, ethanol, and propanol.

(3) The sensitizing solution according to (1) or (2), wherein the Sncompound is at least one kind selected from the group consisting ofSnCl₂, Sn(CH₃COCHCOCH₃)₂, SnBr₂, SnI₂, and SnSO₄.

(4) The sensitizing solution according to any one of (1) to (3), whereinthe sensitizing solution is used for a pretreatment of a body to beplated made from a compound semiconductor.

(5) The sensitizing solution according to any one of (1) to (4), wherein0.001 g/L to 200 g/L of the Sn compound is contained.

(6) An electroless plating method including: a pretreatment process ofimmersing a body to be plated into a pretreatment solution; and aplating process of immersing the body to be plated after being subjectedto the pretreatment process into a plating solution, wherein thesensitizing solution for electroless plating according to any one of (1)to (5) is used as the pretreatment solution.

(7) An electroless plating method including: a pretreatment process ofimmersing a body to be plated into a pretreatment solution; and aplating process of immersing the body to be plated after being subjectedto the pretreatment process into a plating solution, wherein a dilutedsolution obtained by diluting the sensitizing solution for electrolessplating according to any one of (1) to (5), with water and/or an alcoholsolution containing less than 10 vol. % of water-soluble alcohol is usedas the pretreatment solution.

(8) The electroless plating method according to (6) or (7), wherein anactivation process of immersing the body to be plated into an activatingsolution containing a plating catalyst including Pd is performed betweenthe pretreatment process and the plating process.

(9) The electroless plating method according to (6) or (7), wherein theplating process is a silver mirror reaction.

Advantageous Effects of Invention

Since the sensitizing solution for electroless plating according to theinvention contains the Sn compound and the solvent in which the solventcontains 10 vol. % or more of the water-soluble alcohol, the sensitizingsolution can be used for a long period of time without impairing theuniformity of a metal plating coating. In addition, in the sensitizingsolution electroless plating according to the invention, the solvent hasan excellent property of dissolving the Sn compound, so that thesensitizing solution can dissolve the Sn compound without the use ofacid.

In addition, the electroless plating method according to the inventionis a method in which the sensitizing solution for electroless platingaccording to the invention which can be used for a long period of timeis used as the pretreatment solution, so that the uniformity of themetal plating coating is excellent, and variations of quality rarelyresult. In addition, the renewal frequency of the sensitizing solutioncan be reduced, so that industrially high productivity can be obtained.

In addition, in another electroless plating method according to theinvention, when the diluted solution obtained by diluting thesensitizing solution for electroless plating according to inventionwhich can be used for a long period of time with the water and/oralcohol solution containing less than 10 vol. % of water-soluble alcoholis used as the pretreatment solution, in order to enhance preservation,the concentration of the water-soluble alcohol contained in thesensitizing solution is increased to be high so as to be dilutedproperly for use. As a result, the Sn compound is easily dissolved usingthe solvent containing a high concentration of the water-solublealcohol, and a use amount of the water-soluble alcohol contained in thepretreatment solution can be relatively decreased while maintaining along life span of the sensitizing solution, compared to the case wherethe sensitizing solution for electroless plating according to theinvention is used, thereby enhancing safety in the handling of thepretreatment solution.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a picture of bodies to be plated which are subjected toelectroless Ni—P plating using sensitizing solutions of ExperimentalExamples 1 to 4 that are left as they are for 24 hours (1 day).

FIG. 2 is a picture of bodies to be plated which are subjected toelectroless Ni—P plating using the sensitizing solutions of ExperimentalExamples 1 to 4 that are left as they are for 3 days.

FIG. 3 is a picture of bodies to be plated which are subjected toelectroless Ni—P plating using the sensitizing solutions of ExperimentalExamples 1 to 4 that are left as they are for 5 days.

FIG. 4 is a picture of bodies to be plated which are subjected toelectroless Ni—P plating using the sensitizing solution of ExperimentalExample 1 that is left as it is for 7 days and using the sensitizingsolution of Experimental Example 1 that is left as it is for 57 days.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the invention will be described in detail.

Sensitizing Solution

A sensitizing solution for electroless plating according to theinvention contains an Sn compound and a solvent, and the solventcontains 10 vol. % or more of a water-soluble alcohol.

The sensitizing solution for electroless plating according to theinvention can be used for pretreatment of a body to be plated when ametal plating coating is formed on the body to be plated which is madeof a non-conductive material such as glass, ceramic, or plastic otherthan metals, and particularly, can be preferably used for pretreatmentof a body to be plated which is made of a compound semiconductor.

It is preferable that the solvent includes only water-soluble alcohol,or includes water and water-soluble alcohol.

The kind of the water-soluble alcohol is not particularly limited, andis preferably one kind selected from the group consisting of methanol,ethanol, and propanol. It is particularly preferable that ethanol whichcauses the metal plating coating to obtain high adhesion to the body tobe plated, has an excellent property of dissolving the Sn compound, andeffectively lengthens the life span of the sensitizing solution, beused.

The concentration of the water-soluble alcohol contained in the solventis equal to or more than 10 vol. %. However, in order to enhance theproperty of dissolving the Sn compound and lengthen the life span of thesensitizing solution, a higher concentration thereof is more preferable.By increasing the concentration of the water-soluble alcohol containedin the solvent to be equal to or more than 10 vol. %, a sensitizingsolution which can be used for 3 days or longer can be obtained.

It is preferable that the Sn compound is at least one kind selected fromthe group consisting of stannous chloride (SnCl₂), stannous acetate(Sn(CH₃COCHCOCH₃)₂), stannous bromide(SnBr₂), stannous iodide (SnI₂),and stannous sulfate (SnSO₄). Particularly, it is preferable thatstannous chloride which can cause the metal plating coating to obtainhigh adhesion to the body to be plated and has excellent economicefficiency be used.

The concentration of the Sn compound in the sensitizing solution ispreferably in the range of 0.001 g/L to 200 g/L, more preferably, in therange of 0.001 g/L to 10 g/L, and most preferably, in the range of 0.05g/L to 5 g/L. When the concentration of the Sn compound in thesensitizing solution is less than the above range, there may be a casewhere the effect of the Sn compound in accelerating the adsorption of aplating catalyst onto the body to be plated cannot be sufficientlyobtained. In addition, when the concentration of the Sn compound in thesensitizing solution exceeds the above range, the effect obtained bycontaining the Sn compound cannot be further enhanced, and the life spanof the sensitizing solution is shortened.

Electroless Plating Method

Next, an electroless plating method according to the invention will bedescribed.

First, a body to be plated which is made of glass, ceramic, plastic, orthe like is prepared.

Next, a pretreatment process of immersing the body to be plated into apretreatment solution which is the sensitizing solution according to theinvention is performed. Accordingly, the Sn compound which is anadsorbent material that accelerates the adsorption of the platingcatalyst onto the body to be plated is supplied to the body to be plated(sensitizing treatment).

Moreover, the sensitizing solution according to the invention can beused as the pretreatment solution as it is. However, in a case where theconcentration of the Sn compound in the sensitizing solution is highenough, a diluted solution obtained by diluting the sensitizing solutionwith water and/or an alcohol solution containing less than 10 vol. % ofwater-soluble alcohol may be used.

Specifically, for example, a solution which contains a solvent onlyincluding the water-soluble alcohol and an Sn compound and thus in whichthe concentrations of the Sn compound and the water-soluble alcohol arehigh is used as the sensitizing solution, and a diluted solutionobtained by diluting the sensitizing solution with water such that 0.05g/L to 5 g/L of the Sn compound is contained is preferably used as thepretreatment solution.

Moreover, in the pretreatment process, in order to further enhance theadhesion of the metal plating coating onto the body to be plated bycausing the Sn compound to be effectively adhered to the body to beplated, before immersing the body to be plated into the sensitizingsolution, an alkali treatment for degreasing the surface of the body tobe plated using alkali, an acid treatment using acid such as H₂SO₄, awashing treatment using water, or the like is preferably performed asneeded.

Next, an activation process of immersing the body to be plated afterbeing subjected to the pretreatment process into an activating solutioncontaining the plating catalyst is performed. Accordingly, the platingcatalyst adsorbs onto the body to be plated. As the plating catalyst,those containing Pd, Ag, or Cu may be used. It is preferable that aplating catalyst which contains Pd and thus obtains excellent adhesionbe used. In addition, as the plating catalyst containing Pd, thosecontaining PdCl₂ are preferably used.

Here, the operations of the sensitizing solution in the activationprocess will be described by exemplifying the plating catalyst as thosecontaining Pd. In the activation process, Sn²⁺ ions contained in thesensitizing solution react with Pd²⁺ ions contained in the platingcatalyst as follows and thus become Sn⁴⁺ ions, so that Pd precipitates.Pd generated here adsorbs onto the body to be plated as a nucleus ofelectroless plating.

Sn²⁺+Pd²⁺→Sn⁴⁺+Pd⁰

Moreover, in the activation process, in order to further enhance theadhesion of the metal plating coating onto the body to be plated, it ispreferable that a washing treatment using water be performed beforeand/or after immersing the body to be plated into the activatingsolution.

In addition, it is preferable that processes from the pretreatmentprocess to the activation process performed on the body to be plated berepeated several times in order to cause the plating catalyst to adsorbonto the body to be plated more reliably without staining.

The number of repetitions is, more preferably, 3 in order to obtain asufficient effect without causing disruptions in the manufacturingprocesses.

Thereafter, a plating process of immersing the body to be plated afterfinishing the pretreatment process and the activation process into aplating solution is performed.

Here, as metals to be plated electrolessly on the body to be plated,there are Ni-based, Cu-based, Co-based, and Sn-based metals, and thelike. Examples of the plating solution and a plating process conditionsused here are described as follows.

Electroless Ni—P Plating (in the Case of Glass as the Body to be Plated)

NiSO₄•6H₂O 0.05 mol NH₂CH₂COOH 0.15 mol NaH₂PO₂•H₂O 0.20 mol Pb 0.1 ppmpH 4.5 Bath temperature 60° C.

Electroless Copper Plating

CuSO₄•5 H₂O 0.03 mol (copper sulfate) EDTA•4 Na 0.24 mol(ethylenediaminetetraacetic acid sodium) HCHO 0.20 mol (formaldehyde) 2,2′-bipyridine  10 ppm (2,2′-bipyridine) PEG-1000 100 ppm(polyethyleneglycol) Bath temperature 60° C. pH 12.5

Dissolved oxygen is controlled to 2 to 4 ppm while performing airagitation

Electroless Co Plating

Cobalt sulfate 0.08 mol Sodium hypophosphite 0.2 mol Sodium tartrate 0.5mol Borate 0.5 mol pH 9.0 Bath temperature 90° C.

The sensitizing solution according to this embodiment contains the Sncompound and the solvent, and the solvent contains 10 vol. % or more ofthe water-soluble alcohol, so that the Sn compound can be easilydissolved without the use of acid. Therefore, the sensitizing solutioncan be used for a long period of time without impairing the uniformityof the metal plating coating.

In addition, in the sensitizing solution according to this embodiment,in the case where the water-soluble alcohol is ethanol, high adhesion ofthe metal plating coating onto the body to be plated can be obtained,and the life span of the sensitizing solution can be effectivelylengthened.

In addition, in the sensitizing solution according to this embodiment,in the case where the Sn compound is SnCl₂, high adhesion of the metalplating coating onto the body to be plated can be obtained.

In addition, in the electroless plating method according to thisembodiment, since the sensitizing solution for electroless platingaccording to this embodiment which can be used for a long period of timeis used as the pretreatment solution, the uniformity of the metalplating coating is excellent and thus variations in quality rarelyresult, and the renewal frequency of the sensitizing solution can bereduced, thereby obtaining industrially high productivity.

In addition, in the electroless plating method according to thisembodiment, in the case where the diluted solution obtained by dilutingthe sensitizing solution for electroless plating according to thisembodiment with the water and/or alcohol solution containing less than10 vol. % of the water-soluble alcohol is used as the pretreatmentsolution, in order to enhance preservation, the concentration of thewater-soluble alcohol contained in the sensitizing solution is increasedto be high so as to be diluted properly for use. As a result, the Sncompound is easily dissolved using the solvent containing a highconcentration of the water-soluble alcohol, and a use amount of thewater-soluble alcohol contained in the pretreatment solution can berelatively decreased while maintaining a long life span of thesensitizing solution, compared to the case where the sensitizingsolution for electroless plating according to the invention is used,thereby enhancing safety in the handling of the pretreatment solution.

Moreover, in the above-described embodiment, the case where the body tobe plated is subjected to the activation process after the pretreatmentprocess so as to be plated with metals such as Ni-based, Cu-based,Co-based, and Sn-based metals using electroless plating is exemplified.However, the invention is not limited to the embodiment. For example,the activation process may not be performed, and the body to be platedmay be immersed into a plating solution containing precious metal suchas Ag-based or Au-based metal in a plating process so as to be platedwith the precious metal using electroless plating. Examples of theplating solution and a plating process conditions used here aredescribed as follows.

Electroless Silver Plating

AgNO₃ 0.03 mol Glucose 0.025 mol Ammonia 0.15 mol KOH 0.06 mol Bathtemperature 50° C.

Electroless Gold Plating

NaAuCl₄ 0.012 mol Na₂S₂O₃ 0.1 mol Na₂SO₃ 0.1 mol NH₄Cl 0.05 mol SodiumL-ascorbate 0.25 mol pH 6.0 Temperature 60° C.

Here, in a case where a silver mirror reaction is performed in theplating process without the activation process, the operation of thesensitizing solution in the silver mirror reaction is described. In theplating process, Sn²⁺ ions contained in the sensitizing solution reactwith Ag¹⁺ ions contained in the plating solution as follows and becomeSn⁴⁺ ions, so that Ag precipitates. Ag generated here adsorbs onto thebody to be plated as a nucleus of electroless plating.

Sn²⁺+Ag¹⁺→Sn⁴⁺+Ag⁰

Even in the case where the silver mirror reaction is performed in theplating process, as in the case where metals such as Ni-based, Cu-based,Co-based, and Sn-based metals are electrolessly plated on the body to beplated by performing the activation process after the pretreatmentprocess, the sensitizing solution for electroless plating according tothis embodiment which can be used for a long period of time is used asthe pretreatment solution. Therefore, the uniformity of the metalplating coating is excellent and thus variations in quality rarelyresult, and the renewal frequency of the sensitizing solution can bereduced, thereby obtaining industrially high productivity.

EXAMPLES

Hereinafter, the invention will be described in detail on the basis ofExamples. Moreover, the invention is not limited to Examples.

Experimental Example 1

A sensitizing solution of Example 1 was obtained by dissolving 0.1 g ofstannous chloride (SnCl₂. 2H₂O) in 1 liter of pure ethanol (EtOH). Inthe sensitizing solution of Example 1, an Sn compound could be easilydissolved at a concentration of 0.1 g/L without the use of acid.

Experimental Examples 2 to 4

Sensitizing solutions (diluted solutions) of Experimental Examples 2 to4 were obtained under the same conditions as those of Example 1 exceptthat the sensitizing solution (stock solution) that could be obtained bydissolving 10.0 g of stannous chloride (SnCl₂.2H₂O) in 1 liter of pureethanol (EtOH) was diluted with water so that the concentrations ofethyl alcohol were 10 vol. % (Experimental Example 2), 1 vol. %(Experimental Example 3), and 0.1 vol. % (Experimental Example 4).

Moreover, the concentration of the Sn compound in the sensitizingsolution of Example 2 was 1.0 g/L, the concentration of the Sn compoundin the sensitizing solution of Example 3 was 0.1 g/L, and theconcentration of the Sn compound in the sensitizing solution of Example4 was 0.01 g/L.

Using the sensitizing solutions of Experimental Examples 1 to 4 thatcould be obtained as described above and which were left as they werefor 24 hours, electroless Ni—P plating was performed on the bodies to beplated as follows.

First, the bodies to be plated which were made of glass were subjectedto ultrasonic cleaning in pure water for 5 minutes, an alkali treatmentfor degreasing the surfaces of the bodies to be plated using 3 mass % ofcaustic soda was performed for 5 minutes, an acid treatment using 3 mass% of H₂SO₄ was performed for 1 minute, and then a washing treatmentusing water was performed.

Thereafter, a pretreatment process of immersing the bodies to be platedinto pretreatment solutions which are the sensitizing solutions ofExperimental Examples 1 to 4 for 1 minute was performed. Next, thebodies to be plated after being subjected to the pretreatment processwere washed with water and immersed into activating solutions for 1minute. Then, an activation process of washing the bodies to be platedafter being subjected to the activation process with water wasperformed. Thereafter, processes from the pretreatment process to theactivation process performed on the bodies to be plated were performed 3times.

As the activating solution, a solution obtained by dissolving 1 g ofPdCl₂ in a solvent containing 10 milliliters of HCl and 4 liters ofwater was used.

Thereafter, a plating process of immersing the bodies to be plated afterfinishing the pretreatment process and the activation process into theplating solution used in the above-mentioned “Electroless Ni—P Plating”(in the case of glass as the body to be plated) under conditions of pH4.5 and a bath temperature of 60° C. for 30 minutes was performed. Theresults are shown in FIG. 1.

FIG. 1 is a picture of the bodies to be plated which were subjected tothe electroless Ni—P plating using the sensitizing solutions ofExperimental Examples 1 to 4 that were left as they were for 24 hours (1day). As shown in FIG. 1, any of the sensitizing solutions ofExperimental Examples 1 to 4 could obtain uniform metal platingcoatings.

In addition, the bodies to be plated were subjected to the electrolessNi—P plating under the same conditions as those of the case using thesensitizing solutions that were left as they were for 1 day except thatthe sensitizing solutions of Experimental Examples 1 to 4 that were leftas they were for 3 days were used. The results are shown in FIG. 2.

FIG. 2 is a picture of the bodies to be plated which were subjected tothe electroless Ni—P plating using the sensitizing solutions ofExperimental Examples 1 to 4 that were left as they were for 3 days. Asshown in FIG. 2, in Experimental Examples 1 and 2 containing 10 vol. %or more of ethanol, uniform metal plating coatings could be obtained.However, in Experimental Example 3 containing 1 vol. % of ethanol, thedeposit ratio of the metal plating coating was about 30% although theconcentration of the Sn compound was the same as that in ExperimentalExample 1. In addition, in Experimental Example 4 containing 0.1 vol. %of ethanol, the deposit ratio of the metal plating coating was about20%.

From the result, it could be seen that using the sensitizing solutioncontaining 10 vol. % or more of ethanol, the life span of thesensitizing solution could be effectively lengthened.

In addition, the bodies to be plated were subjected to the electrolessNi—P plating under the same conditions as those of the case using thesensitizing solutions that were left as they were for 1 day except thatthe sensitizing solutions of Experimental Examples 1 to 4 that were leftas they were for 5 days were used. The results are shown in FIG. 3.

FIG. 3 is a picture of the bodies to be plated which were subjected tothe electroless Ni—P plating using the sensitizing solutions ofExperimental Examples 1 to 4 that were left as they were for 5 days. Asshown in FIG. 3, in Experimental Example 1, a uniform metal platingcoating could be obtained. However, in Experimental Examples 2 to 4, thedeposit ratios of metal plating coatings were equal to or less than 30%.

In addition, the bodies to be plated were subjected to the electrolessNi—P plating under the same conditions as those of the case using thesensitizing solutions that were left as they were for 1 day except thatthe sensitizing solution of Experimental Example 1 that was left as itwas for 7 days and the sensitizing solution of Experimental Example 1that was left as it was for 57 days were used. The results are shown inFIG. 4.

FIG. 4 is a picture of the bodies to be plated which were subjected tothe electroless Ni—P plating using the sensitizing solution ofExperimental Example 1 that was left as it was for 7 days and using thesensitizing solution of Experimental Example 1 that was left as it wasfor 57 days. As shown in FIG. 4, in Experimental Example 1, both thesensitizing solutions that were left for 7 days and 57 days as they werecould obtain uniform metal plating coatings.

From the results, it could be seen that the life span of the sensitizingsolution of Experimental Example 1 was very long.

Experimental Examples 5 to 8

Sensitizing solutions of Experimental Examples 5 to 8 were obtainedunder the same conditions as those of Experimental Example 1 except thatmethanol (Experimental Example 5), propanol (Experimental Example 6),ethylene glycol monoethyl ether (cellosolves) (Experimental Example 7),and lactate (Experimental Example 8) were used instead of ethanol.

In the sensitizing solutions of Examples 5 to 8, Sn compounds could beeasily dissolved without the use of acid.

In addition, bodies to be plated were subjected to the electroless Ni—Pplating under the same conditions as those of Experimental Example 1except that the sensitizing solutions of Experimental Examples 5 to 8that were left as they were for 1 day were used.

As a result, in Experimental Example 5 using methanol and ExperimentalExample 6 using propanol, uniform metal plating coatings could beobtained. However, in Experimental Example 7 using cellosolves andExperimental Example 8 using lactate, adhesion of metal plating coatingsonto the bodies to be plated was insufficient.

INDUSTRIAL APPLICABILITY

The invention can be applied to a sensitizing solution for electrolessplating and an electroless plating method, and more particularly, to asensitizing solution for electroless plating which can be used for along period of time without impairing the uniformity of a metal platingcoating, and an electroless plating method using the same.

1. A sensitizing solution for electroless plating comprising: an Sncompound; and a solvent, wherein the solvent contains 10 vol. % or moreof a water-soluble alcohol.
 2. The sensitizing solution according toclaim 1, wherein the water-soluble alcohol is at least one kind selectedfrom the group consisting of methanol, ethanol, and propanol.
 3. Thesensitizing solution according to claim 1, wherein the Sn compound is atleast one kind selected from the group consisting of SnCl₂,Sn(CH₃COCHCOCH₃)₂, SnBr₂, SnI₂, and SnSO₄.
 4. The sensitizing solutionaccording to claim 1, wherein the sensitizing solution is used for apretreatment of a body to be plated made from a compound semiconductor.5. The sensitizing solution according to claim 1, wherein 0.001 g/L to200 g/L of the Sn compound is contained.
 6. An electroless platingmethod comprising: a pretreatment process of immersing a body to beplated into a pretreatment solution; and a plating process of immersingthe body to be plated after being subjected to the pretreatment processinto a plating solution, wherein the sensitizing solution forelectroless plating according to claim 1 is used as the pretreatmentsolution.
 7. An electroless plating method comprising: a pretreatmentprocess of immersing a body to be plated into a pretreatment solution;and a plating process of immersing the body to be plated after beingsubjected to the pretreatment process into a plating solution, wherein adiluted solution obtained by diluting the sensitizing solution forelectroless plating according to claim 1, with water and/or an alcoholsolution containing less than 10 vol. % of water-soluble alcohol is usedas the pretreatment solution.
 8. The electroless plating methodaccording to claim 6, wherein an activation process of immersing thebody to be plated into an activating solution containing a platingcatalyst including Pd is performed between the pretreatment process andthe plating process.
 9. The electroless plating method according toclaim 6, wherein the plating process is a silver mirror reaction.